One of the characteristic behaviors of plastic (or viscoelastic) materials is the creep phenomenon, which is defined as the continuing deformation under a constant load with time. Although research on creep of plastic pipes has been widely carried out in other plastics, little work has been reported for creep in ABS (acrylonitrilebutadiene-styrene) pipes at high temperatures. In this paper, the generalized Kelvin series of formulae, which consists of six Kelvin elements, a power model, as well as logarithmic regressions, are applied to the experimental data measured from creep tests under constant bending stresses at different temperatures for two ABS resins. The least-squares method was used to adjust the Kelvin model parameters, and a Levenberg-Marquardt non-linear least-squares regression procedure was used to determine the creep parameters in the power model. This led to empirical formulae for creep compliance defined as the reciprocal of the creep modulus. This creep modulus can provide a means to evaluate the long-term structural properties for different resins used in pipe production.